Field of the Invention
This invention is concerned in general with the removal of organic impurities from aqueous media such as potable water supplies using molecular sieve adsorbents. More particularly, the invention involves the treatment of aqueous media to remove organic contaminants present in relatively low concentrations, i.e., from about 10 parts per billion by weight (ppb) up to about 20,000 parts per million by weight (ppm), by selective adsorption thereof on an organophilic molecular sieve and the subsequent partial or complete oxidation of the adsorbed organic species by contact with a solution of a strong oxidizing agent.
Discussion of the Prior Art
The contamination of supplies of potable water is a major public health concern throughout the world. Sources of ground water contamination are many and varied and include land fills, agricultural pesticides, leakage from stored gasoline, septic tanks, mining operations, petroleum and natural gas production and improperly constructed and maintained industrial toxic waste dumps. The discharge of chlorinated organics into the environment, is a cause of particular concern because of the known or suspected carcinogenic or mutagenic properties of some of these materials and the difficulty with which they are biologically digraded. In many instances chlorinated and other halogenated organic compounds pass through conventional industrial or municipal wastewater treatment plants essentially unaltered.
Several techniques have heretofore been proposed to detoxify or treat contaminated water, principal among which are the so-called air stripping procedure and the method involving the adsorption of the organic values on granulated activated carbon (GAC adsorption). The air stripping process involves stripping the volatile organics from water by contacting the contaminated water with air, most commonly in a countercurrent manner in a packed tower. Contaminated water is introduced at the top of the tower and as it flows down the tower, the volatile organics are stripped off by air that is flowing upwards following introduction at the bottom of the tower. The treated "clean" water is withdrawn at the bottom. A serious disadvantage with this technique is that the air, that is now contaminated with stripped off organics, is discharged into the atmosphere from the top of the tower. The organic pollutants are thus merely transferred from water to air. The technique, therefore, does not get rid of the undesirable pollutants. Other disadvantages to the method are the inability to deal with non-volatile contaminents such as certain pesticides, and the tendency for the stripping tower to be affected by biological growth.
GAC adsorption processes are capable of removing both volatile and non-volatile contaminants from aqueous media, but require expensive high carbon usage to obtain a purified water having non-detectable levels of impurity. Also the adsorption system is cumbersome to regenerate and, in any event, causes a secondary pollution problem in the disposal of the adsorbed impurities. A combination of both types, i.e. the air-stripping and the GAC adsorption process is disclosed in U.S. Pat. No. 4,544,488 issued Oct. 1, 1985 to R. P. O'Brien. Other processes are disclosed in U.S. Pat. No. 4,526,692 issued July 2, 1985 to T. L. Yohe and U.S. Pat. No. 4,517,094 issued May 14, 1985 to G. W. Beall. It is also well known to disinfect or sanitize aqueous media such as recirculating water systems, effluents from food processing industries, paper mills, sewage stations and the like by the introduction of very strong oxidizing agents such as ozone. In this regard see U.S. Pat. No. 4,541,944 issued Sept. 17, 1985 to Sanderson.